The following invention relates generally to instrumentalities for cutting bone during surgery. More particularly, the instant invention is directed to a high speed surgical saw which uses a drive mechanism to move a surgical saw blade (cutting blade) back and forth at a high frequency. The drive mechanism is needed to impart a back and forth motion to the cutting blade and may be, for example, a reciprocating, semi-oscillating, rotational or ultrasound drive. The surgical saw blade may have a cutting action in a longitudinal, orthogonal or rotary in relation to the drive mechanism. The surgical saw blade may have a distal portion having at least one pair of teeth configured to be adjacent to each other and each of the pair of teeth having a cutting edge which is oriented with the teeth so that the cutting edge is disposed away from a centrally positioned longitudinal axis between the teeth. A gullet is then formed between the teeth, creating a cavity along the longitudinal axis of the ultrasound horn.
Typical procedures requiring bone removal or resection include surgeries to repair injuries such as orthopedic surgeries or back surgeries, as well as surgeries to access other tissues such as temporary skull resection to access the brain or vertebrae removal to access a spinal cord.
One of the most vexing problems that surgeons face when using ultrasound surgical saws when cutting bone tissue is the rapid temperature rise of the saw blade due to the accumulation of bone chips within the area of the saw teeth. Since tissue necrosis quickly occurs at temperatures greater than 75° C. (degrees centigrade), a rapid temperature rise of an ultrasound surgical saw is a significant problem which may injure or destroy the bone tissue itself as well as other adjacent tissues. The problem is particularly significant since while working the surgeon can neither see nor feel whether he has caused damage, which only becomes subsequently apparent.
When such necrosis occurs, the tissue does not grow into the cut site, fracture site, or surface of the cement-less prosthesis or other prosthesis and may fail to knit. In the absence of knitting, the prosthesis may not be anchored by bone growth, possibly resulting in the necessity to have a replacement operation some period of years thereafter. In some instances, half of all knee or hip operations may be revision procedures, often because in the initial operation, where temperature is a contributing factor, excessive temperatures were reached at the site of the shaped surface or bone kerf (or cut).
An accumulated bone chip grit trapped within the teeth of a saw blade tends to get vibrated at ultrasonic frequencies. This is known to cause the temperature of a saw blade and surrounding tissue to increase very quickly. This effect may limit the use of a device to a maximum period of less than 1-minute before a surgeon must stop cutting to avoid tissue necrosis due to overheating.